Traveling in search of the rare ingredient, “sky fish” Meliodas and Hawk arrive at a palace that floats above the clouds. The people there are busy preparing a ceremony, meant to protect their home from a ferocious beast that awakens once every 3,000 years. But before the ritual is complete, the Six Knights of Black—a Demon Clan army—removes the seal on the beast, threatening the lives of everyone in the Sky Palace.

With the help of the "Dragon Sin of Wrath" Meliodas and the worst rebels in history, the Seven Deadly Sins, the "Holy War", in which four races, including Humans, Goddesses, Fairies and Giants fought against the Demons, is finally over. At the cost of the "Lion Sin of Pride" Escanor's life, the Demon King was defeated and the world regained peace. After that, each of the Sins take their own path.

Tristan, the son of Meliodas and Elizabeth, inherits the power of the Goddess Clan and can heal people’s wounds and injuries, but he often ends up hurting others due to his inability to control his Demon Clan power. To protect his family, Tristan heads to Edinburgh Castle and meets a host of new friends along the way.

Reunited with Lancelot for the first time since their tragic accident, Tristan must learn to conquer his inner demons in order to save his mother's life.